Crystals, growth of, in silica gel

It has long been observed that very beautiful crystals sometimes develop in gels. Wonderfully fine crystals of sugar frequently grow in ordinary fruit jellies. Many splendid mineral crystals are embedded in silica and appear to have developed while the silica was in the state of a gel. For this geological aspect of the subject, consult the papers of Cornu in the first five volumes of Kolloid-Zeitschrift. The experiments on crystal growth require some time for the proper development of the crystals, but the technique of the method is very simple and easily acquired. 

Zeolite ZSM-23 can be readily synthesized with pyrrolidine as organic template and fumed silica as silica source. Pyrrolidine seems to intervene in the nucleation and crystal growth process, in the latter case most probably as pore-filling agent. By proper optimization of the gel composition and the synthesis conditions, ZSM-23 can be synthesized in less than one day. The synthesis of ZSM-23 has some... 

Rubin, B. (1969) Growth of single crystals by controlled diffusion in silica gel. AIChEJ, 15, 206-208. 

Van Rosmalen, G.M., Marchee, W.G.J. and Bennema, P. (1976) A comparison of gypsum crystals grown in silica gel and agar in the presence of additives. Journal of Crystal Growth, 35, 169-176. 

Kurien, K. V. Ittyachen, M. A. (1979). Growth kinetics and habit modification of barium molybdate single crystals in silica gel.. Cryst. Growth. 47., 5-6., (November-December 1979) 743-745, ISSN 0022-0248. 

Silica membranes have also been studied by several investigators for use in gas separation and membrane reactors. They arc thermally very sublc up to about 500°C. Sintering and densification temperatures of silica membranes depend on the water/alkoxide ratio in the sol-gel process for making the membranes (Langlct et al., 1992]. Crystallization of amorphous silica particles in the membranes takes place at temperatures around 1,000°C [Larbot et al., 1989]. However, pore growth can gradually... 

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